Optical die with variable refractive index, adaptive of angle of incidence, and method of fabricating such a die

ABSTRACT

An optical die, which is intended to be placed in front of an optical sensor of a semiconductor component, has an optically useful zone having an optical axis and exhibiting a variable refractive index. Specifically the refractive index of the die is variable in an annular peripheral zone lying between a radius Ru enveloping the useful zone and a smaller radius Ro. The index is varies as a function of radial distance from a higher value near the smaller radius Ro to a lower value near the radius Ru. The function of the variable refractive index lies between a maximum and minimum profile.

PRIORITY CLAIM

The present application claims priority from French Application for Patent No. 08 54469 filed Jul. 2, 2008, the disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION Technical Field of the Invention

The present invention relates to the field of optical modules intended to be placed in front of optical sensors of semiconductor components and more particularly the field of optical modules or dies intended to be placed in front of optical sensors of semiconductor components.

SUMMARY OF THE INVENTION

According to one mode, a die may comprise an optically useful zone having an optical axis and exhibiting a variable refractive index, so that it is smaller in its peripheral part than in its just adjacent interior part or in its central part.

In an annular peripheral zone, lying between a radius Ru enveloping the useful zone and a smaller radius Ro, the refractive index may lie between a maximum profile Pmax and a minimum profile Pmin.

The maximum profile Pmax may be such that between the radius Ro and a radius R2 the maximum refractive index is equal to a value n₁ and then that between this radius R2 and the radius Ru, the value of the maximum refractive index is defined, as a function of the distance from the center of the die r, by the formula

$n = {n_{1} - {\left( {n_{1} - n_{3}} \right) \cdot \frac{\left( {r - R_{2}} \right)^{2}}{\left( {R_{u} - R_{2}} \right)^{2}}}}$

The minimum profile Pmin may be such that between the radius Ro and a radius R1, the value of the minimum refractive index is defined, as a function of the distance from the center of the die r, by the formula

$n = {n_{2} - {\left( {n_{2} - n_{0}} \right) \cdot \frac{\left( {r - R_{0}} \right)^{2}}{\left( {R_{1\;} - R_{0}} \right)^{2}}}}$

and than that between this radius R1 and the radius Ru the minimum refractive index is equal to a value n₀.

The values of the refractive indices may be such that n₁ is greater than n₀, n₂ lies between n₀ and n₁, and n₃ lies between n₀ and n₂.

The values of the radii may be such that R1 lies between Ro and Ru and R2 lies between Ro and Ru.

For example, n₂ may be equal to n₀ plus 8/10 of (n₁−n₀) and n₃ may be equal to ½ of (n₁+n₀).

For example, Ro may be equal to ⅗ of Ru, R1 may be equal to Ro plus ⅓ of (Ru−Ro) and R2 may be equal to Ro plus ⅞ of (Ru−Ro).

According to one embodiment, implanted ions may determine the variant of a refractive index.

Moreover, grooves and/or through-holes situated outside the said useful zone may be made in the die.

According to another mode, a method of making a die may comprise the following steps: making at least one mask on the central zone delimited by the radius Ro of at least one face of the die, or at least one mask outside this central part, and immersing the die in an ion bath so as to implant ions contained in this bath in the zones not covered by the said mask.

A method may comprise the following steps: making at least one second mask different from the first mask, and immersing the die in a second ion bath so as to implant ions of this bath through the zones not covered by the said second mask.

A method may comprise a step of rediffusion of the implanted ions.

The implantation may possibly be carried out under the effect of an acceleration electric field.

According to another embodiment, an optical semiconductor device may comprise a semiconductor component exhibiting an optical sensor and, in front of this optical sensor, an optical module comprising a die as defined above.

In an embodiment, an apparatus comprises a transparent optical die having front and rear parallel surfaces and having a rectangular optically useful zone centered on an optical axis and a central circular zone within the optically useful zone and also centered on the optical axis, the transparent optical die having a variable refractive index at least in a region of the transparent optical die located between an outer edge of the central circular zone and an extent of the optically useful zone.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the invention will become apparent on examining the detailed description of modes of implementation and embodiments, wholly non-limiting, and the appended drawings in which:

FIG. 1 represents a radial cut through a device comprising a die;

FIG. 2 represents a view from above of a die;

FIG. 3 represents a graph of profiles of maximum and minimum refractive indexes;

FIG. 4 represents a first exemplary embodiment of a refractive index profile;

FIG. 5 represents a second exemplary embodiment of a refractive index profile;

FIG. 6 represents a third exemplary embodiment of a refractive index profile;

FIG. 7 represents a fourth exemplary embodiment of a refractive index profile;

FIG. 8 represents a view from above of a die equipped with a mask;

FIG. 9 represents a radial cut through the die of FIG. 8;

FIG. 10 represents a view from above of the die of FIGS. 8 and 9 after a treatment;

FIG. 11 represents a radial cut through the die of FIG. 10;

FIG. 12 represents a graph of the profile of the refractive index of the die of FIGS. 10 and 11;

FIG. 13 represents a radial cut through a die equipped with a mask;

FIG. 14 represents a cut through the die of FIG. 13 after a treatment;

FIG. 15 represents a graph of the profile of the refractive index of the die of FIG. 14;

FIG. 16 represents a radial cut through a die equipped with a mask;

FIG. 17 represents a cut through the die of FIG. 16 after a treatment;

FIG. 18 represents a graph of the profile of the refractive index of the die of FIG. 17;

FIG. 19 represents a radial cut through a die equipped with a mask;

FIG. 20 represents a cut through the die of FIG. 19 after a treatment; and

FIG. 21 represents a graph of the profile of the refractive index of the die of FIG. 20.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, it may be seen that represented therein is a stack 1 comprising a semiconductor component 2, for example flat and with a square contour, exhibiting at the center of a face 3 an optical sensor 4, for example rectangular, and an optical module 5 placed in front of the face 3, in contact with or a very small distance from this face by virtue of a peripheral spacing ring 3 a, and intended to focus the light rays towards the optical sensor 4.

The optical module 5 can comprise a transparent die 6, for example made of glass, with parallel faces and a square contour corresponding to that of the semiconductor component 2. It may possibly furthermore comprise an optical lens 7 placed in front of the die 6, possibly with interposition of a diaphragm 8 and of a peripheral spacing ring 8 a.

As shown in FIG. 2, the die 6 may exhibit an optically useful rectangular zone 9 corresponding to the optical sensor 4 and exhibiting the same optical axis 10 situated at the center.

It may be advantageous for the die 6 to exhibit a refractive index n, considered in relation to any radial plane, that can vary over at least an annular part between its center 10 and the periphery of its useful zone 9, being smaller in its peripheral part than in its just adjacent interior part or in its central part.

In particular, the value of the refractive index n, considered in relation to any radial plane, may be variable over an annular peripheral zone 11 lying approximately between a radius Ru enveloping the useful zone 9 and a smaller radius Ro.

The radius Ru may be approximately equal to half a diagonal of the useful zone 9, whereas the radius Ro may for example be approximately equal to at least half the small side of the useful zone 9. Thus, the variation in the value of the refractive index may be more particularly achieved in the corners of the useful zone 9.

As shown by FIG. 3, in the annular peripheral zone 11, the profile of the refractive index, considered in relation to any radial plane, may lie between a maximum profile Pmax and a minimum profile Pmin that are such as defined hereinbelow.

(a) the maximum profile Pmax may be such that between the radius Ro and a radius R, the value of the maximum refractive index is equal to a value n₁ and then that between this radius R2 and the radius Ru, the value of the maximum refractive index is defined, as a function of the distance from the center of the die r, by the formula

$n = {n_{1} - {\left( {n_{1} - n_{3}} \right) \cdot \frac{\left( {r - R_{2}} \right)^{2}}{\left( {R_{u} - R_{2}} \right)^{2}}}}$

(b) the minimum profile Pmin may be such that between the radius Ro and a radius R1, the value of the minimum refractive index is defined, as a function of the distance from the center of the die r, by the formula

$n = {n_{2} - {\left( {n_{2} - n_{0}} \right) \cdot \frac{\left( {r - R_{0}} \right)^{2}}{\left( {R_{1} - R_{0}} \right)^{2}}}}$

and then that between this radius R1 and the radius Ru the value of the minimum refractive index is equal to a value n₀,

moreover, the above refractive indices may be defined with respect to one another in the following manner:

n₁ may be greater than n₀,

n₂ may lie between n₀ and n₁,

n₃ may lie between n₀ and n₂,

Moreover, the above radii may be defined with respect to one another in the following manner:

R1 may lie between Ro and Ru,

R2 may lie between Ro and Ru.

Various relative values could be adopted. Nevertheless, the following relative values are proposed:

n₂ may be equal to n₀ plus 8/10 of (n₁−n₀),

n₃ may be equal to ½ of (n₁+n₀),

Ro may be equal to ⅗ of Ru,

R1 may be equal to Ro plus ⅓ of (Ru−Ro),

R2 may be equal to Ro plus ⅞ of (Ru−Ro).

Moreover, in practice, n0 may lie between 85 and 99% of n₁.

Considering the above relative values, examples of index gradients obtained in annular zones 11 of dies 6 and lying between the profiles Pmax and Pmin will now be given.

Referring to FIG. 4, it may be seen that represented therein is a refractive index profile 12 for a die 6 treated in such a way that this refractive index 12 is at the value n₁ between the radius Ro and a radius Ra lying between the radii R1 and R2, and then, starting off tangentially, inflects while decreasing down to the value n₀ at the radius Ru.

Referring to FIG. 5, it may be seen that represented therein is a refractive index profile 13 for a die 6 treated in such a way that this refractive index 13 is at the value n₁ between the radius Ro and a radius Ra, lying between the radii Ro and R1, is at the value n₀ between a radius Rb, lying between the radius R1 and the radius R2, and the radius Ru and forms an inverted S joining them between Ra and Rb, meeting up with them tangentially.

Referring to FIG. 6, it may be seen that represented therein is a refractive index profile 14 for a die 6 treated in such a way that this refractive index profile 14 is approximately identical to that of FIG. 5 between the radii Ra and Ru but is distinguished therefrom by the fact that between Ra and Ro, it inflects, decreasing down to a value n₄ lying between n₁ and n₂, starting off tangentially to n₁ at the radius Ra.

Referring to FIG. 7, it may be seen that represented therein is a refractive index profile 15 for a die 6 treated in such a way that this refractive index profile 15 is approximately identical to that of FIG. 5 between the radii Ro and Rb but is distinguished therefrom by the fact that between Rb and Ru it inflects, increasing up to a value n₅ lying between n₀ and n₃, starting off tangentially to n₀ at the radius Rb.

Referring to FIGS. 8 to 21, the way in which a die 6 may be treated in order to obtain for example any one of the refractive index gradients hereinabove will now be described.

To obtain the refractive index gradient 12 of FIG. 4, it is possible to proceed as follows.

As shown by FIGS. 8 and 9, it is possible to start from a die 6.0 exhibiting a refractive index n₀, for example uniformly doped with sodium ions.

Masks 16 covering the die and exhibiting a central orifice in the form of a disc of radius greater than or equal to Ra, that is to say not covering the zone inside the radius Ra, are made on the opposite faces thereof, for example by photolithography.

The die 6.0 is immersed in an ion bath to obtain ion diffusion in the material of the die 6, which can be accelerated through the effect of an electric field. The conditions of such treatment are suited to the refractive index gradient 12 to be obtained.

For example, ions of thallium or of silver may be implanted.

The masks 16 may then be removed.

As shown by FIGS. 10, 11 and 12, a die 6.1 is obtained whose refractive index is at the value n₁ in its central part and up to the radius Ro, and then its refractive index follows the profile of the gradient 12 between the radii Ra and Ru.

According to a variant execution applied to exchanges of different ions, to obtain a corresponding refractive index profile, it would be possible to make a reverse mask, that is to say make a mask on the central part of the die 6.0, perform an implantation from outside and then a diffusion towards the interior.

To obtain the refractive index gradient 13 of FIG. 5, it is possible to start from the die 6.1 treated as hereinabove and to apply thereto, in the presence or absence of the masks 16, a suitable complementary treatment of high temperature ion rediffusion.

In this case, as shown by FIGS. 14 and 15, a die 6.2 is obtained whose refractive index is at the value n₁ in its central part and up to the radius Ro, and then its refractive index follows the profile of the gradient 13 up to the radius Rb, and is then at the value n₀ up to the radius Ru.

To obtain the refractive index gradient 14 of FIG. 6, it is possible to start from the die 6.1 treated and ridded of the masks 16 and, as shown by FIG. 16, it is possible to make, on the faces of this die 6.1, masks 17 covering the faces of the die and leaving open a ring corresponding approximately to the zones 19 going from the radius Ro to a radius greater than Ra.

The die 6.1 is immersed in an ion bath to obtain ion diffusion in the material of this die, which can be accelerated through the effect of an electric field. The conditions of such a treatment are suited to the refractive index gradient 14 to be obtained.

For example, thallium ions may be implanted.

As shown by FIGS. 17 and 18, a die 6.3 is obtained whose refractive index follows the profile of the gradient 14.

Here again, it would be possible to use a reverse mask.

To obtain the refractive index gradient 15 of FIG. 7, it is possible to start from the die 6.1 treated and ridded of the masks 16 and, as shown by FIG. 19, it is possible to make, on the opposite faces of this die 6.1, masks 20 in the form of discs going approximately up to a radius greater than or equal to Rb.

This die 6.1 is immersed in an ion bath to obtain an ion diffusion in the material of this die, which can be accelerated through the effect of an electric field. The masks 20 are then removed.

For example, it is possible to implant ions of thallium or of silver.

A thermal rediffusion could also be carried out.

As shown by FIGS. 20 and 21, a die 6.4 is obtained whose refractive index follows the profile of the gradient 15.

Here again, a reverse mask could be used.

The various profiles of refractive index gradients just described are certainly not the only ones which could be achieved while remaining within the template defined by the profiles Pmax and Pmin. Likewise, the operating modes could be different and the materials and baths used could be different.

The die 6 may advantageously stem from a wafer in which a large number of dies are made simultaneously.

For this purpose, the aforesaid masks are then formed on the wafer at the locations of the dies to be obtained. The ion implantations and the other treatments, if any, are carried out through the opposite faces of this wafer. Grooves and/or through holes can thus be made in the wafer, outside the optically useful zones 9 of the locations, so as to perform the ion implantations and the other treatments, if any, in particular through the flanks of these grooves and/or through-holes.

The treatments of the wafer having been performed, the said wafer is then sawn along perpendicular lines so as to individualize each die 6 treated.

Starting from an original optical module including a transparent die with substantially constant refractive index, such that the light rays which pass through it exhibit, on the periphery of the sensor, too high an angle of incidence for the image to be captured correctly, the die treatments as described make it possible to decrease this angle of incidence, according to a desired gradient. Such an arrangement may make it possible to reduce the amplitude of an original positive distortion, principally in its periphery, of the captured image.

Although preferred embodiments of the method and apparatus of the present invention have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims. 

1. Apparatus, comprising: an optical module for placement in front of a semiconductor optical image sensor, the optical module comprising a transparent optical die having front and rear parallel surfaces and having a rectangular optically useful zone centered on an optical axis of the semiconductor optical image sensor and a central circular zone within the optically useful zone and also centered on the optical axis, the transparent optical die having a variable refractive index at least in a region of the transparent optical die located between an outer edge of the central circular zone and an extent of the optically useful zone.
 2. The apparatus of claim 1 wherein the variable refractive index in the region varies as a function of radial distance from the optical axis.
 3. The apparatus of claim 2 wherein the function for varying the variable refractive index is substantially the same for all radial planes extending from the optical axis.
 4. The apparatus of claim 1 wherein a radius of the central circular zone is approximately one-half a shortest side length of the rectangular optically useful zone.
 5. The apparatus of claim 2 wherein the transparent optical die has a substantially constant refractive index within the central circular zone.
 6. The apparatus of claim 1 wherein the variable refractive index in the region varies from a first, relatively higher, refractive index at the outer edge of the central circular zone towards a second, relatively lower, refractive index for radial distance farther from the optical axis than the outer edge of the central circular zone.
 7. The apparatus of claim 1 wherein the variable refractive index decreases with radial distance from the optical axis in the region located between the outer edge of the central circular zone and the extent of the optically useful zone.
 8. An optical die for use within an imaging optical module to be placed in front of an optical sensor of a semiconductor component, comprising: an optically useful zone having an optical axis aligned with the optical sensor and exhibiting a variable refractive index which is smaller in its peripheral part than in its just adjacent interior part or in its central part and which, in an annular peripheral zone lying between a radius Ru enveloping the useful zone and a smaller radius Ro, lies between a maximum profile Pmax and a minimum profile Pmin; (a) the maximum profile Pmax being such that between the radius Ro and a radius R2 the maximum refractive index is equal to a value n₁ and then that between this radius R2 and the radius Ru, the value of the maximum refractive index is defined, as a function of the distance from the center of the die r, by the formula $n = {n_{1} - {\left( {n_{1} - n_{3}} \right) \cdot \frac{\left( {r - R_{2}} \right)^{2}}{\left( {R_{u} - R_{2}} \right)^{2}}}}$ (b) the minimum profile Pmin being such that between the radius Ro and a radius R1, the value of the minimum refractive index is defined, as a function of the distance from the center of the die r, by the formula $n = {n_{2} - {\left( {n_{2} - n_{0}} \right) \cdot \frac{\left( {r - R_{0}} \right)^{2}}{\left( {R_{1} - R_{0}} \right)^{2}}}}$ and then that between this radius R1 and the radius Ru the minimum refractive index is equal to a value n₀; (c) and in which: n₁ is greater than n₀, n₂ lies between n₀ and n₁, n₃ lies between n₀ and n₂, R1 lies between Ro and Ru, R2 lies between Ro and Ru.
 9. The die according to claim 8, in which: Ro is equal to ⅗ of Ru, R1 is equal to Ro plus ⅓ of (Ru−Ro), R2 is equal to Ro plus ⅞ of (Ru−Ro).
 10. The die according to claim 9, in which: n₂ is equal to n₀ plus 8/10 of (n₁−n₀), n₃ is equal to ½ of (n₁+n₀).
 11. The die according to claim 8, in which implanted ions determine the variation in a refractive index.
 12. The die according to claim 8, further comprising grooves and/or through-holes situated outside the said useful zone.
 13. A method, comprising: making at least one first mask relative to a central zone of a die of transparent optical material, the central zone being delimited by a radius Ro, the first mask having a first radius, and immersing the die in an ion bath so as to implant ions contained in this bath in zones of the die which are not covered by the first mask.
 14. The method according to claim 13, comprising: making at least one second mask different from the first mask, the second mask having a second radius different from the first radius, and immersing the die in a subsequent second ion bath so as to implant ions of this bath in zones of the die not covered by the second mask.
 15. The method according to claim 14, further comprising a rediffusion of the implanted ions.
 16. The method according to claim 13, further comprising a rediffusion of the implanted ions.
 17. The method according to claim 13, wherein the ions are implanted under the effect of an acceleration electric field.
 18. An optical semiconductor device, comprising: a semiconductor component having a rectangular optical sensor with an optical axis; and an optical module placed in front of the optical sensor, the optical module comprising: a transparent optical die having front and rear parallel surfaces and having a rectangular optically useful zone corresponding in size and shape to the rectangular optical sensor and centered on the optical axis and a central circular zone within the optically useful zone and also centered on the optical axis, the transparent optical die having a variable refractive index at least in a region of the transparent optical die located between an outer edge of the central circular zone and an extent of the optically useful zone.
 19. The device of claim 18, wherein the optical module further comprises a lens positioned adjacent the front parallel surface of the transparent optical die.
 20. The device of claim 18 wherein the transparent optical die has a substantially constant refractive index within the central circular zone.
 21. The device of claim 18 wherein the variable refractive index decreases with radial distance from the optical axis in the region located between the outer edge of the central circular zone and the extent of the optically useful zone. 